The present invention generally relates to a vacuum sintering furnace for sintering a pre-compacted workpiece of metal powder, and more particularly to a vacuum sintering furnace including a first section for first eliminating lubricant contained in the workpiece, a second section for subsequently sintering the workpiece, and a third section for cooling the sintered workpiece.
As is well known, the workpiece of metal powder to be compacted generally contains the lubricant such as zinc stearate and paraffin wax by about 1 wt %. The lubricant serves to reduce the friction to be caused between the particles of the metal powder during the compacting process so as to produce a uniform compact. Therefore, the lubricant contained in the compacted workpiece is generally eliminated prior to the sintering process in order to avoid such a problem that the lubricant of the workpiece is vaporized due to the heat for the sintering and adheres onto the cooling surface of the furnace body so as to be solidified in layers.
According to a prior art, the lubricant eliminating process is effected in a specific furnace completely separated from the sintering furnace. Thus, the prior art has such disadvantages that it takes a long time to handle the workpiece in the lubricant eliminating furnace and to carry it into the sintering furnace, and since the workpiece is cooled to some extent when it is discharged out of the lubricant eliminating furnace before the charging of the workpiece into the sintering furnace, a great amount of heat loss is caused so that the fuel costs become high.